Question

For the gas phase reaction
$PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right)$
Which of the following conditions are correct ?

• A. $\Delta H<0and\Delta S<0$
• B. $\Delta H>0and\Delta S<0$
• C. $\Delta H=0and\Delta S<0$
• D. $\Delta H>0and\Delta S>0$

Answer 1

Answer: (D)

$\Delta H>0and\Delta S>0$

Given gas phase reaction is :-

${PCl}_5\left(g\right)\rightleftharpoons {PCl}_3\left(g\right)+{Cl}_2\left(g\right)$

we know that,

$△H=△H+△ngRT$

Here $△H=$ Erthalpy change of reaction

$△E=$ internal energy change of reaction

$△ng=$ difference in no. of moles of gaseous products and reactants.

Here, $△ng=1+1-1=1>0$

so, $△H>0$

& $△S=$ S product - Sreactant $>0$